The present invention relates to a blood collecting needle, and more particularly, to a blood collecting needle which is capable of making one or more blood collections after a being for blood collection is connected to a storage chamber which has previously been placed at a negative pressure.
In the prior art, blood collecting units by which a plurality of blood collections are made possible with one piercing are frequently used when performing clinical tests. These units, for example, as shown in FIG. 5, comprise cannulas 120 and 130 disposed at both ends of a hub 110, a blood collecting needle 100 having an elastic sheath 135 mounted so as to surround the cannula 130, a cylindrical holder 200 in which the blood collecting needle 100 is fixedly mounted, and a blood collecting tube 300 which is inserted into this holder 200 and placed at a negative pressure (evacuated pressure) beforehand. A rubber or a gass-barrier stopper is inserted into the blood collecting tube 300 so that the inside thereof is maintained at a negative pressure. When collecting blood, first a holder 200 and a blood collecting needle 100 are assembled into one piece. A cannula 120 is made to pierce an intravenous vein and the intravenous vein is secured. The blood collecting tube 300 is pushed into the holder, and the cannula 130 is caused to pass through the elastic sheath 135 and the rubber stopper 310. As a result, blood collection is started and completed in a state in which the pressure inside the blood collecting tube 300 is balanced with the intravenous pressure.
However, in such a conventional vacuum blood collecting system, it is impossible to confirm a so-called flashback, since there is no place where any gas inside the cannula or the elastic sheath can escape when an intravenous vein is pierced and before the blood collecting tube 300 is pushed into the holder. For this reason, there is a danger that blood collection will sometimes start when the cannula pierces at a position other than the intravenous vein.
To solve such a problem, a needle assembly equipped with a mechanism capable of confirming this flashback is proposed in Japanese Patent Publication for Opposition (KOKOKU) No. 2-21809 (Priority of U.S. patent application Ser. No. 645,893, filed on Aug. 31, 1984, now U.S. Pat. No. 4,679,571).
However, the needle assembly proposed therein is very complex in construction, as it comprises a venting apparatus as a communicating path disposed inside the hub, ring-like compressed sleeves which are inserted into a communicating path disposed inside the apparatus and has drawbacks, such as swelling due to water content, etc. This presents a problem in that it cannot be mass-produced inexpensively. In the needle of the present invention, a negative pressure is applied to sleeves housed inside the housing at the time blood is collected. The needle cannot be fully sealed from the outside, lacks adequate safety precautions, and has a lot of dead volume.